Single engine aircraft are a substantial majority of the total national fleet. It has been determined that these aircraft can achieve performance and load carrying capabilities comparable with small twin engine aircraft. Many of the features normally associated with high performance aircraft are being provided in single engine airframes. Such features include pressurization, six place seating, high altitude capability (e.g., turbo charging), and prop and wing deicing systems. The single feature, common in twin engine aircraft, and unavailable in single engine aircraft, is weather radar. Weather radar is considered a safety essential by many pilots for transit through areas experiencing convective activity (thunder storms). Without the capabilities of radar, the capabilities of a single engine aircraft as an all-weather transportation machine are seriously compromised.
The normal position for mounting the radome and radar antenna is in the otherwise unoccupied nose section of twin engine aircraft. In single engine aircraft, this same general area is occupied by the engine, propeller, and accessories. Accordingly, in attempting to provide satisfactory radar capabilities for single engine aircraft, various manufacturers have proposed radome and radar antenna locations other than the nose section. For example, in one such prior art radar system, the aircraft wing is structurally modified to accommodate a radar antenna and radome in the leading edge of the wing. In such installation, space constraints dictate the use of a generally elipsoidal cross-section. The reflector is pivoted with respect to the wave guide to scan the radar. Thus, other than at the straight-ahead orientation, the reflector is at a less than optimum relationship with the wave guide. The disadvantages of such a system include long required cable lengths between the antenna and electronics, structural modification of the wing, relatively low range, and poor definition, due to the antenna configuration.
Another prior art single engine radar system incorporates a wing mounted pod in which the radome and radar antenna are mounted. Such a wing mounted radome alters the flight characteristics of the aircraft and is a source of substantial drag. To minimize the drag increase, the antenna size must also be minimized, resulting in poorer than normal radar performance. The highly curved radome necessitated by the aerodynamic characteristics of the enclosure has relatively poor radar transmitting efficiency. Particularly on high wing aircraft, the wing pod mount also subjects the crew and passengers to a higher than normal microwave radiation exposure. The radiation is produced by the side lobe or secondary lobes, prominent in compromise antenna designs.
Some of the deficiencies of the prior art systems could be overcome if the radome and antenna could be located on a portion of the aircraft providing space for a radome of conventional size and configuration and forward of the crew and passengers. The engine cowl of the aircraft has never been utilized for this purpose, presumably because of the interference with the propeller arc and other requirements, such as the engine air induction system in the space available. In such a location, radar energy hitting the propeller would include the components of the primary lobe and high energy level would be reflected directly back into the cockpit. The reflected energy would also produce an extremely high signal level which could damage receiver components. Finally, the prop reflected energy would be interpreted by the receiver as a ground or storm return and would create "holes" in the display detracting from its accuracy and interpretability.